1. Field of the Invention
This invention relates to carburetors for gas turbine engine combustors and, more particularly, to such carburetors having primary and secondary air swirlers and designed for mounting in combustor domes.
2. Description of Related Art
Gas turbine engine combustors include carburetors for mixing fuel with compressed air to form an air/fuel mixture for combustion in a combustion zone of the combustor. One type of conventional gas turbine engine combustor includes radially spaced outer and inner combustor liners surrounding the combustion zone and joined at an upstream end thereof by a combustor dome. The combustor dome is typically made of sheet metal and is part of a combustor dome assembly that includes a plurality of circumferentially spaced carburetors therein, with each carburetor including a fuel injector for providing fuel and an air swirler for providing swirled air for mixing with the fuel for creating a fuel/air mixture discharged into the combustion zone between the two liners.
The mixture is burned for generating combustion gases which flow downstream or aftwardly through the combustor to a turbine nozzle suitably joined to the aft end of the combustor. Immediately downstream of the turbine nozzle is a high-pressure turbine which extracts energy from the combustion gases for powering a compressor disposed upstream of the combustor which provides compressed air to the engine.
Each of the carburetors includes forward and aft air swirlers respectively, also referred to as primary and secondary swirlers, respectively, having a longitudinal carburetor axis. The aft swirler includes a septum which defines a primary venturi of the carburetor. The aft swirler includes a plurality of circumferentially spaced aft swirl vanes and an annular exit cone, all formed together in an integral casting. The forward swirler includes a ferrule for slidably supporting a fuel injector. The forward swirler includes a plurality of circumferentially spaced forward swirl vanes and a flat annular radial flange attached thereto.
The radial flange of the forward swirler is slidably retained against a forward facing surface of the septum of the aft swirler by a retainer attached to the septum. The retainer has a wide aperture in the middle allowing it to slide over the forward swirl vanes and engage an outer edge of the flat annular radial flange which is wider than the aperture. A ridge along a periphery of the retainer extends aftwardly from an aft face of the retainer. A small notch machined into the ridge receives a narrow anti-rotation tab extending radially outwardly from a periphery of the radial flange of the forward swirler.
The ridge of the retainer is brazed, welded, or otherwise bonded or attached to the forward facing surface of the septum. This secures the forward swirler to the aft swirler while allowing for differential thermal growth between the fuel injector and the combustor dome while preventing relative rotation between the forward and aft swirlers. This helps set, control, and maintain desirable Pattern Factors.
The retainer is formed from a retainer casting and its final shape including the ridge and notch features are machined into the retainer casting. The primary swirler typically has a narrow anti-rotation tab that engages the notch to prevent relative rotation between the primary and secondary swirlers. The narrow tab is subject to fretting from engine cycles and, thus, prone to failure. The primary and secondary swirlers and the retainer are delicate and prone to damage during fabrication and from handling during assembly and maintenance and from engine operating loads. The primary and secondary swirlers and retainer plate are extensively machined at their mating surfaces which is costly. It is, thus, desirable to provide a carburetor and its parts that are not as delicate and prone to damage during fabrication and from handling and during engine operation from vibratory engine operating loads.